The hellishly hot conditions in some Minneapolis classrooms last week represent the district's push to boost achievement by opening school a week early clashing with the reality of an aging district not fully equipped to deal with record heat.

Although St. Paul and some inner-ring suburbs also report some or most of their classrooms lack cooling, they didn't start until after Labor Day. That day's high temperature is about two degrees cooler on average than the day when Minneapolis students logged in for the year.

With one Minneapolis school dating to the 19th century, the question facing Minneapolis is whether it's worth retrofitting the nearly half of its 71 aging schools that lack full air conditioning. A capital planning study that's not yet finished estimates the 10-year cost to complete air conditioning of schools that have classrooms without it at between $275 million and $350 million, including inflation. That price poses some hard questions for a school board and district that already may need to build classrooms to handle rising enrollment and is in the middle of a program to replace worn-out building systems.

The alternative to adding cooling is for the district to hope for cool weather for pre-Labor Day starts while laying contingency plans to divert district staff to deliver ice, Popsicles and fans to the hardest-hit school, as they did last week.

That's the approach the district said that it would use when it defended its decision to start before Labor Day for a fifth straight year, something it said would give students more days on task before statewide math, reading and science tests each spring. But some questioned how much is getting done last week.

"There's no learning happening," said Stephanie Pichner, the mother of two Loring Community School students. She held her first-grader out of school last Tuesday after a first day in which he seemed on the verge of illness when water failed to arrive.

After holding school Monday through Wednesday last week in record or near-record heat, the district canceled classes Thursday and Friday in its 27 schools without air conditioning.

Some students in older first-ring districts don't need to beat the heat in school, even if it's still hot when they went back this week. All classrooms in Robbinsdale are air-conditioned, even those in the district's oldest school, built in 1954. Most classrooms are air-conditioned in the St. Anthony-New Brighton district. But in Edina, most schools have just a few rooms with cooling; the oldest building, Concord Elementary, got a systems upgrade this summer with venting and dehumidification improvements, but no air conditioning.

In St. Paul, only 21 of the district's 69 schools have full or partial air conditioning, a smaller proportion than Minneapolis. But the district hasn't been tempted to try an early start because the complications of the State Fair make that unfeasible, according to spokeswoman Toya Stewart Downey.

Aside from charter schools that have more freedom in their starting dates, the biggest bloc of early-starting schools is in southwestern Minnesota, where 22 districts serving more than 15,000 students jointly shifted 10 days from the end of their calendars to before Labor Day, using flexible school year latitude the Legislature granted.

Their motive was the same as Minneapolis — to put more days before tests. Some dismissed students early last week, but Redwood Falls area schools Superintendent Rick Ellingworth said both buildings in his district have been air-conditioned for the last 15 years. Twenty-one of the 40 schools in the consortium are cooled.

But instead of districts moving school into hotter weeks to prep for tests, couldn't the state just let districts test later in the school year? Charlene Briner, chief of staff for the Minnesota Department of Education said teachers anecdotally report that student concentration wanes as the weather warms. Delaying testing until late May or early June also would make it hard to meet the Legislature's requirement to report test results by Oct. 1, she said.

In Minneapolis, the question of adding air conditioning comes atop a backlog of $650 million in deferred maintenance identified in 2011, a burden that the district has only just begun addressing at a pace of $50 million annually. That's before considering a potential building program to handle enrollment that's growing by about 1 percent annually, and weighing the cost of upgrading schools to current standards. The estimated cost of adding air conditioning would be the single most costly category of those renovations, according to Chief Administrative Officer Mark Bollinger, so expensive that he broke it out separately for the board to consider later this year.

Although the district is replacing worn-out cooling equipment where it exists, sometimes it gets added to old buildings. The $6.1 million renovation of the 1927 Howe building, which reopened last week eight years after it last held students, added rooftop air-conditioning units as part a major redo of mechanical systems and other major improvements.

But at much-larger Edison, a mechanical renovation will include venting to handle air conditioning, but the chiller units to make it operational may not come for several years.

Adding cooling to an 1898 building like Pratt Community School, where the community has successfully resisted several attempts to close the small Prospect Park school, will be even more challenging. That's because it has radiant heat and lacks the vents needed to handle cool air. Moreover, other upgrades, such as the electrical system, likely will also be needed, Bollinger said.

Indeed, concern over overloading aging electrical is one reason that the district this week refused to let parents bring in window units to cool classrooms of sweltering students.

Steve Brandt • 612-673-4438

Twitter: @brandtstrib